The present invention relates to a bearing made of an aluminum alloy.
Recently, the application of aluminum alloy to power equipment has widely been examined for reducing the power equipment in weight. Of aluminum alloys, hyper-eutectic Al--Si alloy which is superior in abrasion resistance and seizure resistance has drawn attention in the application to the bearing part of a power equipment. A conventional hyper-eutectic Al--Si alloy is superior in abrasion resistance, but in some cases may be inferior in a so-called running-in (wearing-in) characteristic. Herein, running-in characteristic of a bearing material is defined as a quality thereof showing the extent to which a process for obtaining its mild abrasion proceeds. Furthermore, running-in of a bearing material is herein defined as an abrasion process thereof until its mild abrasion following its initial severe abrasion is obtained. In other words, if a bearing material is inferior in running-in characteristic, its initial severe abrasion continues and is not followed by its mild abrasion, during the frictional action of a moving member supported by the bearing, under a condition of inferior lubrication or under a condition where powder generated by abrasion (hereinafter referred to as "abrasion powder") is hardly removed from the interface between the bearing and the moving member. Thus, the abrasion powder remaining between the bearing and the moving member accelerates their abrasion and may cause abnormal abrasion thereof. In contrast, if a bearing material is superior in running-in characteristic, its initial severe abrasion is followed by its mild abrasion. During the initial severe abrasion, wavy and uneven surfaces of the bearing and of the moving member (e.g., shaft) wear away. With this, contact area between the bearing and the moving member increases, and thus the pressure exerted on the bearing by the moving member decreases and vice versa. In this way, the initial severe abrasion changes to the mild abrasion.
In general, a bearing made of a harder material relative to the moving member's material is inferior in the running-in characteristic. In view of this, there have been proposals to form a solid lubricant (e.g., lead, tin and molybdenum disulfide) layer on the bearing surface and to form an oil groove thereon for forcibly supplying oil. However, these proposals require additional steps and costs in the bearing preparation. Thus, there has been a demand for a bearing which is superior in abrasion resistance, seizure resistance and running-in characteristic, and is prepared without using these proposals.